The present invention relates to a reading-out apparatus for reading out features such as characters, marks, etc. recorded or labeled on box, card, etc. by processing a video signal obtained by scanning the features.
Such reading-out apparatus is generally used for a pattern recognition. As for a picking-up apparatus which generates video signal by scanning an object, two dimensional picking-up apparatus such as raster scanning type flying spot scanner, television camera, image detector, etc., and one dimensional picking-up apparatus such as solid image sensor, line scanning type flying spot scanner, etc. are widely used. In case of using two dimensional picking-up apparatus, it is not necessary to move the object and the picking-up apparatus relatively. But in case of using one dimensional picking-up apparatus, it is necessary to move the object, for example, in a direction perpendicular to a scanning one. In order to decrease errors in pattern recognition by performing precise reading-out procedure by means of either one or two dimensional picking-up apparatus, the video signal thus obtained must be processed adequately. For instance, it is generally carried out to convert the video signal thus obtained into black and white binary signal so as to compare this signal with a given threshold value. In one case, the threshold level is fixed, but in another case the threshold level is variable corresponding to the video signal level. In case of using variable threshold method it is possible to carry out more precise reading-out procedure than in case of fixed threshold method. In the usual variable threshold level method, an input video signal is integrated so as to obtain an average level and then the threshold level is determined according to the average level thus obtained. Such a method is fully applicable when the average level of the video signal changes relatively slowly, but is not always applied if the video signal level changes abruptly. For example, in case of reading-out characters, marks, etc. which are recorded or labeled on box, card, etc., a video signal amplitude changes abruptly at an edge of box, card, label, etc., so that it is difficult to perform the correct reading-out procedure by the known method mentioned above. Especially, in case of reading out a color printing on box, card, label, etc., the video signal level is fairly variable according to the color.
Moreover, in case of using an automatic reading-out apparatus the detected video signal must be converted into a binary signal. For this purpose a plurality of slice levels must be set up on the basis of the threshold level, and then each slice level thus obtained is compared with the input video signal. If the method of using the plurality of slice levels is combined with the variable threshold method, it is expected to perform more precise reading-out procedure. However, in such a method, since a pitch between successive slice levels and thus, a span of whole slice levels are made constant, it is not possible to carry out the precise reading-out procedure by only varying the standard level such as the threshold level.